Upconversion fluorescence property of Er/Yb-codoped novel bismuth-germanium glass

Infrared-to-visible upconversion fluorescence property of Er³⁺/Yb³⁺-codoped novel bismuth-germanium glass under 975 nm LD excitation has been studied. Intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs. The structure of the bismuth-germanium glass has been investigated by peak-deconvolution of FT-Raman spectrum, and the structural information was obtained from the peak wavenumbers. This novel bismuth-germanium glass with low maximum phonon energy (∼750 cm⁻¹) can be used as potential host material for upconversion lasers.     

Comparative investigation of up-conversion luminescence in Tm/Yb-codoped germanate-niobic and germanium-bismuth glasses: effect of phonon density on up-conversion emission

Tm³⁺/Yb³⁺-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions ¹G₄→³H₆ and ¹G₄→³H₄, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency.     

Structural and upconversion fluorescence properties of Er/Yb-codoped oxychloride lead-germanium-bismuth glass

Structural and infrared-to-visible upconversion fluorescence properties of Er³⁺/Yb³⁺-codoped oxychloride lead-germanium-bismuth glass have been studied. The Raman spectrum investigation indicates that PbCl₂ plays an important role in the formation of glass network, and has an important influence on the upconversion luminescence owing to lower phonon energy. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation.     

Composition dependent frequency upconversion luminescence in Er-doped oxychloride germanate glasses

Er³⁺-doped oxychloride germanate glasses have been synthesized by conventional melting and quenching method. Structural and thermal stability properties were obtained based on the Raman spectra and differential thermal analysis, indicating that PbCl₂ plays an important role in the formation of glass network and has an important influence on the maximum phonon energy and thermal stability of host glasses. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively, were observed at room temperature. With increasing PbCl₂ content, the intensity of green (525 and 546 nm) emissions increases significantly, while the red (657 nm) emission increases slowly. The results indicate that PbCl₂ has more influence on the green emissions than the red emission in oxychloride germanate glasses. The possible upconversion luminescence mechanisms has also been estimated and discussed.     

Upconversion luminescence and mechanisms in Yb-sensitized Tm-doped oxyhalide tellurite glasses

Effect of Yb₂O₃ content on upconversion luminescence and mechanisms in Yb³⁺-sensitized Tm³⁺-doped oxyhalide tellurite glasses were investigated under 980 nm excitation. Intense blue and relatively weak red upconversion emission centered at 476 and 649 nm corresponding to the transitions ¹G₄→³H₆ and ¹G₄→³H₄ of Tm³⁺, respectively, are simultaneously observed at room temperature. The results show that upconversion blue and red emission intensities of Tm³⁺ first increase, reach its maximum at Yb₂O₃%=3 mol%, and then decrease with increasing Yb₂O₃ content. The effect of Yb₂O₃ content on upconversion intensity is discussed, and possible effect mechanisms are evaluated. The investigated results were conducing to increase upconversion luminescence efficiency of Tm³⁺.     

Role of Yb and Tm ions in upconversion emission of Tb under 798 and 980 nm laser excitations in Tb-Tm-Yb doped tellurite glass

Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb³⁺: ⁵D₄ → ⁷F₆, ⁷F₅, ⁷F₄, ⁷F_J (J = 0, 1, 2, 3) and Tm³⁺: ¹G₄ → ³H₆, ¹G₄ → ³F₄, ³F₃ → ³H₆, ³H₄ → ³H₆ transitions, respectively. Among Tm³⁺, Yb³⁺and Tb³⁺ ions only Tm³⁺ has a ground state absorption at 798 nm excitation due to ³H₄ ← ³H₆ transition. For 980 nm excitation only Yb³⁺ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm³⁺ ions are excited which excite Yb³⁺ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb³⁺ ions to Tm³⁺ and Tb³⁺ ions takes place. Under 980 nm excitation Yb³⁺ ions absorb the incident energy and excite Tm³⁺ and Tb³⁺ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb³⁺, Tm³⁺ and Tb³⁺ has been studied. The lifetime of the ¹G₄ level has also been measured.     

Spectral performance and intensive green upconversion luminescence in Er/Yb-codoped NaY(WO4)2 crystal

Using Czochralski (CZ) pulling method, an Er³⁺/Yb³⁺-codoped NaY(WO₄)₂ crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd-Ofelt (J-O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: ⁴G_11/2 + ⁴I_9/2 → ²H_11/2 (or ⁴S_3/2) + ²H_11/2 (or ⁴S_3/2), and ⁴G_11/2 + ⁴I_15/2 → ²H_11/2 (or ⁴S_3/2) + ²I_13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer ⁴G_11/2(Er³⁺) + ²F_7/2(Yb³⁺) → ⁴F_9/2(Er³⁺) + ²F_5/2(Yb³⁺) was also demonstrated.     

Infrared-to-red upconversion luminescence in samarium-doped antimony glasses

A new antimony-based glass system (K₂O-B₂O₃-Sb₂O₃) having low phonon energy (about 600 cm⁻¹) doped with Sm³⁺ ions has been developed. Infrared reflection spectroscopic (IRRS) studies have been employed to establish its low phonon energy. Ultraviolet-Visible-near infrared (UV-Vis-NIR) absorption and photoluminescence upconversion properties with the spectrochemistry of the 15K₂O-15B₂O₃-70Sb₂O₃ (mol%) glasses have been studied doping with different concentrations (0.1-1.0 wt%) of Sm₂O₃. UV-Vis-NIR absorption band positions have been justified with quantitative calculation of nephelauxetic parameter and covalent bonding characteristics of the host. NIR to visible upconversion has been investigated by exciting at 949 nm at room temperature. Three upconverted bands originating from the ⁴G_5/2→⁶H_5/2, ⁴G_5/2→⁶H_7/2 and ⁴G_5/2→⁶H_9/2 transitions are found to be centered at 566 (green, weak), 602 (orange, weak) and 636 (red, remarkably strong) nm, respectively. These bands have been explained from the evaluation of the absorption, normal (downconversion) fluorescence and excitation spectra. The upconversion processes have been explained by the excited state absorption (ESA), energy transfer (ET) and cross-relaxation (CR) mechanisms involving population of the metastable (storage) energy level (⁴G_5/2) by multiphonon deexcitation effect. It is evident from the IRRS study that the upconversion phenomena are expedited by the low multiphonon relaxation rate in antimony glasses owing to their low phonon energy (602 cm⁻¹, the main and highest intensity Sb-O-Sb stretching band) which is very close to that of fluoride glasses (500-600 cm⁻¹).     

Spectral analysis of Pr-, Sm- and Dy-doped transparent GeO2-BaO-TiO2 glass ceramics

In this paper, we present the photoluminescence properties of Pr³⁺-, Sm³⁺- and Dy³⁺-doped germanate glasses and glass ceramics. From the X-ray diffraction measurement, the host glass structure was determined. These glasses have shown strong absorption bands in the near-infrared (NIR) region. Compared to Pr³⁺-, Sm³⁺- and Dy³⁺-doped glasses, their respective glass ceramics have shown stronger emissions due to the Ba₂TiGe₂O₈ crystalline phase. For Pr³⁺-doped glass and glass ceramic, emission bands centered at 530 nm (³P₀→³H₅), 614 nm (³P₀→³H₆), 647 nm (³P₀→³F₂) and 686 nm (³P₀→³F₃) have been observed with 485 nm (³H₄→³P₀) excitation wavelength. Of them, 647 nm (³P₀→³F₂) has shown bright red emission. Emission bands of ⁴G_5/2→⁶H_5/2 (565 nm), ⁴G_5/2→⁶H_7/2 (602 nm) and ⁴G_5/2→⁶H_9/2 (648 nm) for the Sm³⁺:glass and glass ceramic, with excitation at ⁶H_5/2→⁴F_7/2 (405 nm) have been recorded. Of them, ⁴G_5/2→⁶H_7/2 (602 nm) has shown a bright orange emission. With regard to the Dy³⁺:glass and glass ceramic, a bright fluorescent yellow emission at 577 nm (⁴F_9/2→⁶H_13/2) has been observed, apart from ⁴F_9/2→⁶H_11/2 (667 nm) emission transition with an excitation at 454 nm (⁶H_15/2→⁴I_15/2) wavelength. The stimulated emission cross-sections of all the emission bands of Pr³⁺, Sm³⁺ and Dy³⁺:glasses and glass ceramics have been computed based on their measured full-width at half-maxima (FWHM, Δλ) and lifetimes (τ_m).     

Spectroscopic investigation of Tm:TeO2-WO3 glass

We studied the spectroscopic characteristics of telluride glass with the host composition (0.85)TeO₂-(0.15)WO₃, containing 0.25 and 1.0 mol% thulium oxide (Tm₂O₃). By analyzing the absorption spectra with the Judd-Ofelt theory, the average radiative lifetimes of 305±7.5 μs and 1.95±0.02 ms were determined for the ³F₄ and ³H₄ levels, respectively. Measured fluorescence lifetime of the ³F₄ level decreased from 218 to 51 μs for the 0.25 and 1.0 mol% Tm₂O₃ doped samples, respectively, indicating the effect of boosted non-radiative decay at higher doping concentrations. A similar trend was observed for the ³H₄ level, where the fluorescence lifetime decreased from 1.86 ms to 350 μs at these concentrations. The quenching of the 1460 nm (³F₄→³H₄) emission in favor of the 1800 nm (³H₄→³H₆) emission due to cross relaxation was further evident in the fluorescence spectra of the samples. The calculated stimulated emission cross sections (3.73±0.1×10⁻²¹ cm² at 1460 nm and 6.57±0.07×10⁻²¹ cm² at 1808 nm) reveal the potential importance of the Tm³⁺:(0.85)TeO₂-(0.15)WO₃ glass for applications in fiber-optic amplifiers and fiber lasers.     

Multiphoton ultraviolet and visible upconversion luminescence of TmYb co-doped oxyfluoride glass

The ultraviolet upconversion luminescence of Tm³⁺ ions sensitized by Yb³⁺ ions in oxyfluoride glass when excited by a 975 nm diode laser was studied in this paper. One typical ultraviolet upconversion luminescence lines positioned at 362.3 nm was found. It can be attributed to the five-photon upconversion luminescence transition of ¹D₂ → ³H₆. Several visible upconversion luminescence lines at 451.1 nm, (477.9 nm, 462.5 nm), 648.7 nm, (680.5 nm, 699.5 nm) and (777.5 nm, 800.7 nm) were found also, which results from the fluorescence transitions of five-photon ¹D₂ → ³F₄, three-photon ¹G₄ → ³H₆, three-photon ¹G₄ → ³F₄, two-photon ³F₃ → ³H₆ and two-photon ³H₄ → ³H₆ of Tm³⁺ ion, respectively. The theoretical analysis suggests that the upconversion mechanism of the 362.3 nm ¹D₂ → ³H₆ upconversion luminescence is the cross energy transfer of {³H₄(Tm³⁺) → ³F₄(Tm³⁺), ¹G₄(Tm³⁺) → ¹D₂(Tm³⁺)} and {¹G₄(Tm³⁺) → ³F₄(Tm³⁺), ³H₄(Tm³⁺) → ¹D₂(Tm³⁺)} between Tm³⁺ ions. In addition, the upconversion luminescence of ¹G₄ and ³H₄ state results from the sequential energy transfer {²F_5/2(Yb³⁺) → ²F_7/2(Yb³⁺), ³H₄(Tm³⁺) → ¹G₄(Tm³⁺)} and {²F_5/2(Yb³⁺) → ²F_7/2(Yb³⁺), ³F₄(Tm³⁺) → ³F₂(Tm³⁺)} from Yb³⁺ ions to Tm³⁺ions, respectively.     

Effect of composition on the spontaneous emission probabilities, stimulated emission cross-sections and local environment of Tm in TeO2-WO3 glass

Effect of composition on the structure, spontaneous and stimulated emission probabilities of various 1.0 mol% Tm₂O₃ doped (1−x)TeO₂+(x)WO₃ glasses were investigated using Raman spectroscopy, ultraviolet-visible-near-infrared (UV/VIS/NIR) absorption and luminescence measurements.Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f-4f transitions of Tm³⁺ ions. Six absorption bands corresponding to the absorption of the ¹G₄, ³F₂, ³F₃ and ³F₄, ³H₅ and ³H₄ levels from the ³H₆ ground level were observed. Integrated absorption cross-section of each band except that of ³H₅ level was found to vary with the glass composition. Luminescence spectra of the samples were measured upon 457.9 nm excitation. Three emission bands centered at 476 nm (¹G₄→³H₆ transition), 651 nm (¹G₄→³H₄ transition) and 800 nm (¹G₄→³H₅ transition) were observed. Spontaneous emission cross-sections together with the luminescence spectra measured upon 457.9 nm excitation were used to determine the stimulated emission cross-sections of these emissions.The effect of glass composition on the Judd-Ofelt parameters and therefore on the spontaneous and the stimulated emission cross-sections for the metastable levels of Tm³⁺ ions were discussed in detail. The effect of temperature on the stimulated emission cross-sections for the emissions observed upon 457.9 nm excitation was also discussed.     

Upconversion studies in Er doped TeO2-M2O (M=Li, Na and K) binary glasses

The luminescence properties of Er³⁺ doped alkali tellurite [ TeO₂-M₂O (M=Li, Na and K)] glasses are investigated. Infrared to visible upconversion emissions are observed at 410, 525, 550 and 658 nm using 797 nm excitation. These bands are assigned to the ²H_9/2  →⁴I_15/2, ²H_11/2  →⁴I_15/2, ⁴S_3/2  →⁴I_15/2, ⁴F_9/2  →⁴I_15/2 transitions of Er³⁺ respectively. Detailed study reveals that the ²H_9/2  →⁴I_15/2 transition at 410 nm involves a three-step process while the other transitions involve two-steps. Excitation with 532 nm radiation gives additional bands at 380, 404, 475 and 843 nm wavelengths due to the ⁴G_11/2  →⁴I_15/2, ²P_3/2  →⁴I_13/2, ²P_3/2  →⁴I_11/2, and ⁴S_3/2  →⁴I_13/2 transitions, respectively, along with the bands observed on NIR excitation. The fluorescence yield is found to be largest for the TeO₂-Na₂O glass. The lifetime of the ⁴S_3/2 level has been measured for all the three cases and used to explain the upconversion mechanisms. The fluorescence intensity ratio corresponding to the two thermally coupled levels (²H_11/2, ⁴S_3/2) has been used to estimate the temperature of the glass. It is observed that the temperature sensing capacity of TeO₂-Li₂O glass is better than the other two glasses.     

Energy transfer and upconversion luminescence in Tm/Yb co-doped lanthanum-zinc-lead-tellurite glasses

A series of Tm³⁺/Yb³⁺ co-doped lanthanum-zinc-lead-tellurite (TPZL) glasses pumped by a 980 nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Effects of PbO content on the thermal stability, structure and upconversion properties of Tm³⁺/Yb³⁺ co-doped TPZL glasses had been investigated. The efficient visible upconversion fluorescences corresponding to the ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ were observed under 980 nm excitation. The upconversion intensities of blue, red and near infrared emissions in Tm³⁺/Yb³⁺ co-doped TPZL glasses were obviously enhanced with increasing PbO content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. Population density in different levels and coefficients of the energy transfer rate C_Di (i=2, 4, 6) between Tm³⁺ and Yb³⁺ were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients C_D2, C_D4, and C_D6 were determined to be 5.7×10⁻¹⁷, 1.3×10⁻¹⁶ and 8.6×10⁻¹⁷ cm³/s, respectively.     

Investigation of 2.0 μm emission in Tm and Ho co-doped oxyfluoride tellurite glass

This paper reports 2.0 μm emission properties of Tm³⁺/Ho³⁺ co-doped oxyfluoride tellurite glass exited by 808 nm laser diode (LD). Mid-infrared transmittance property of glass was investigated by Fourier transform infrared (FTIR) spectrometer. The real chemical composition of investigated glass was identified by X-ray photoelectric spectroscopy (XPS). Thermal stability of the glass was determined by differential thermal analysis (DTA) measurement. The Judd-Ofelt parameters, spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho³⁺ were calculated based on the absorption spectra by using Judd-Ofelt theory. Results indicate that the maximum 2.0 μm emission intensity attributed to the ⁵I₇→⁵I₈ transition of Ho³⁺ was achieved at 1.5 mol% Tm₂O₃ and 1 mol% Ho₂O₃ concentrations in oxyfluoride tellurite glass. OH⁻ absorption at 3000 cm⁻¹ was greatly depressed by introduction of 10 mol% F⁻. The maximum absorption and stimulated emission cross-section of Ho³⁺ near 2.0 μm are 7.0×10⁻²¹ cm² at 1950 nm and 8.8×10⁻²¹ cm² at 2048 nm, respectively. The calculated radiative lifetime of 4.4 ms for ⁵I₇→⁵I₈ transition and large stimulated emission cross-section of the Tm³⁺/Ho³⁺ co-doped oxyfluoride tellurite glass indicate that the glass has a potential application in efficient 2.0 μm laser.     

Enhanced blue-green-red up-conversion and 1.3-μm emission of Pr/Yb-codoped oxyhalide tellurite glasses with PbCl2 doping

We report on the blue-green-red up-conversion spectroscopic properties of Pr³⁺/Yb³⁺-codoped oxyhalide tellurite glasses upon excitation of a conventional 980 nm laser diode (LD). Significant enhancement of the blue-green-red up-conversion emission intensity has been observed with increasing PbCl₂ doping. The up-conversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. The population of the Pr³⁺ upper ³P₀ emitting level was accomplished through a combination of a ground state absorption, energy transfer and excitated state absorption. 1.3-μm emission in the second telecom window originated from Pr³⁺:¹G₄→³H₅ transition has also been investigated upon excitation at 980 nm LD. The measured peak wavelength and full width at half-maximum of the fluorescent are 1335 nm and ∼100 nm, respectively. An enhanced 1.3μm emission with increasing PbCl₂ doping has also been observed. Codoping of Yb³⁺ significantly enhance both the blue-green-red up-conversion emission and 1.3-μm emission intensity by way of a nonradiative Yb³⁺:²F₅→Pr³⁺:¹G₄ energy transfer.     

Infrared to visible upconversion fluorescence in Yb,Tm:YAG single crystal

Absorption spectrum from 400 to 2000 nm and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb³⁺ and 4 at.% Tm³⁺ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition ¹G₄ → ³H₆, the emission band around 646 nm corresponds to the transition ¹G₄ → ³F₄ of Tm³⁺. Energy transfer from Yb³⁺ to Tm³⁺ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of ¹G₄ level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions ¹G₄ → ³H₆ in YAG doped with Yb³⁺ and Tm³⁺ is potentially useful for blue light output.     

The effect of Y co-doping on the persistent up-conversion luminescence of the ZrO2:Yb,Er nanomaterials

The effect of the defects due to the charge compensation obtained with the yttrium co-doping to the ZrO₂:Yb³⁺,Er³⁺ up-converting phosphors was studied. The materials were prepared with the combustion method. The materials purity was analyzed with the FT-IR spectroscopy. The crystal structure was studied with the X-ray powder diffraction and the crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence was excited at room temperature with an IR-laser at 970 nm. The up-conversion luminescence spectra showed red (650-685 nm) and green emission (520-560 nm) due to the ⁴F_9/2→⁴I_15/2 and (²H_11/2,⁴S_3/2)→⁴I_15/2 transitions of Er³⁺, respectively. Persistent up-conversion luminescence was observed both in the Yb³⁺,Er³⁺ and Y³⁺,Yb³⁺,Er³⁺ doped materials.     

Inhomogeneous broadening of the dynamically split Kramers spectral line and up-conversion in the pair and quartet centers in CaF2:Nd

The site-selective and time-resolved fluorescence laser spectroscopy and kinetic measurements with high spectral and nanosecond temporal resolution was applied to analyze the high-energy wing of the M and N absorption bands of the ⁴I_9/2(1)→⁴G_5/2(1) crystal-field (CF) transition in a CaF₂:Nd³⁺ (0.6 wt%) crystal at 4.2 K. It was found that at helium temperatures the dynamically split spectral line assigned as the ⁴I_9/2(1)→⁴G_5/2(1) (CF) transition of coherently coupled Nd³⁺ ions in the pair M- and quartet N-centers of CaF₂:Nd³⁺ (0.6 wt%) is inhomogeneously broadened. It consists of the pair M- and quartet N-centers with at least 0.1 A variation of the positions of the fluorescence-excitation spectral lines registered at the ⁴F_3/2(1)→⁴I_9/2(1) CF transition. Small fluorescence-lifetimes variation of the ⁴F_3/2 and ⁴D_3/2 levels from the small variation of the distances R between Nd³⁺ ions in the pair is found. At least 2.7% variation of the value of the Nd-Nd distance R in the pair M-center was determined from the lifetime variation of the ⁴F_3/2 manifold with the assumption of a dipole-dipole interaction between the ions in the pair.The energy transfer up-conversion process responsible for the UV fluorescence observed when pumping the ⁴I_9/2(1)→⁴G_5/2(1) transition has been determined.     

Spectroscopic properties of Tm ions in chalcogenide Ge-As-S glass containing minute amount of Ga and CsBr

We have experimentally confirmed that the absorption and emission properties for intra-4f-configurational transitions of Tm³⁺ ions doped in Ge-As-S glass, one of representative chalcogenide glasses, are modified dramatically upon the introduction of minute amount of Ga and CsBr, tantamount to a low doping level. This compositional adjustment makes local chemical environments of Tm³⁺ being rearranged spontaneously without any further thermal treatment applied. The hypersensitive ³H₆ ↔ ³F₄ transition, in particular, turns out to reflect the modified chemical environments more significantly than other transitions. Redistribution of the stark levels of ³F₄ manifold is mainly responsible for the significant changes in emission spectra for ³H₄ → ³F₄ and ³F₄ → ³H₆ transitions. Since the addition of small amount of the group III elements and alkali halides alters only the optical properties of rare-earth ions, while keeping thermal stability of the chalcogenide glass hosts unchanged, our compositional adjustment method would be quite useful for practical applications of rare-earth activated chalcogenide glasses.